The invention concerns an extruder welding device for welding plastic workpieces, having an extruder unit that is equipped with a discharge device for plasticated plastic material, the discharge device having a discharge member that acts on the plastic material and is driven by a motor.
Extruder welding devices of this kind are known in a wide variety of embodiments (cf., for example, DE 32 21 492 C1, DE 42 36 281 C2, EP 0 663 277 A1, DE 38 08 723 C1, DE 38 35 250 C1, DE 36 16 296 A1, DE Unexamined patent application 28 23 171, EP 0 6377 497 A1, DE Utility Model 86 12 130.8, DE 297 18 972.7, DE 298 18 696.9, DE 298 18 757.4). They are used to weld plastic panels or other plastic workpieces.
The known extruder devices comprise an extruder unit having a drive, in the form of or similar to a handheld power drill, that is equipped with an extension unit removably placed thereon. Proceeding substantially in the longitudinal direction through this extension unit is a passthrough channel that has a conveying section having a conveying device, and a plasticating section having a heating device and a discharge device integrated therein. The conveying device is arranged close to the drive, while the plasticating section adjoins the free end of the extruder device. The conveying device has an axially extending conveying screw to which a rotary motion can be imparted by the drive. The conveying section of the passthrough channel extends parallel to the axis of this conveying screw, and is adapted to the diameter of a rod made of thermoplastic material in such a way that the rod, when introduced through an insertion opening, is gripped by the screw teeth of the conveying screw and pulled in and transported in an axial direction parallel to its axis. Multiple conveying sections can also be provided over the periphery of the conveying screw in order to allow rods of different diameters, or multiple wires simultaneously, to be drawn in.
The plasticating section of the passthrough channel is surrounded by an electrical heating device. This ensures that the plastic material of the rod is plasticated, i.e. melted, so that the plastic material emerges through a welding shoe in a plasticated state. The rod is previously reduced in size in a comminuting device arranged between the plasticating section and conveying section, so that it enters the plasticating section in pellet-like form. A comminuting device of this kind can be dispensed with if the plastic material is delivered from the outset in a pelletized state.
To allow the plasticated plastic material to emerge from the welding shoe, the extruder unit contains a discharge device having a discharge member that acts on the plastic material. In most embodiments of such extruder units, the discharge member is configured as a delivery screw, arranged in the passthrough channel of the plasticating section, which is nonrotatably joined to the conveying device for the plastic rod and is accordingly also coupled to the drive. During operation, a rotary motion is imparted to the delivery screw, which thus ensures discharge of the plasticated plastic material.
In another embodiment (cf. DE 298 18 757.4), a delivery screw is omitted. In this case the plasticated plastic material is transported by the advancing plastic rod toward the welding shoe, and discharged there. In this case the conveying screw, which draws in the plastic rod and transports it toward the plasticating section, constitutes the discharge member.
The known extruder units were based on the physical design of handheld power drills, which were then modified and expanded with an extruder attachment. Only electric motors have therefore hitherto been used for drive purposes. Electric motors of this kind have a poor power-to-weight ratio, and are bulky. Both characteristics interfere with handling of the extruder unit, and also are disadvantageous if, for example, it is to be added onto semiautomatic machinery or robots.
It is the object of the invention to configure an extruder welding device of the kind cited initially in such a way that the extruder unit weighs less and occupies less space.
This object is achieved, according to the present invention, by the fact that the motor is configured as at least one fluid motor. Fluid motors of this kind have substantially better power-to-weight and power-to-volume ratios than electric motors. In addition, they are characterized by constant-speed behavior largely independent of the requested torque.
The term xe2x80x9cfluid motorsxe2x80x9d is understood to mean both hydraulic and pneumatic motors. Suitable hydraulic motors are, in particular, hydrostatic drives such as axial-piston, sliding-vane, or rotary-piston motors. A connection to a pressurized fluid source is needed to operate the fluid motors, but it can be separate from the actual extruder unit; the connection between the pressurized fluid source and fluid motor can be created via fluid hoses. Electrically driven hydraulic pumps or compressed-air generators are especially suitable as the pressurized fluid source.
The configuration according to the present invention is suitable for any type of extruder welding unit that has a drive system for discharging the plasticated plastic material. The good power-to-weight and power-to-volume ratios make handling of the extruder unit substantially easier. For this reason, it is also better suited for use in semiautomatic machinery or robots.
In an embodiment of the invention, provision is made for fluid hoses to be attached to the fluid motor in order to supply it with a fluid, e.g. hydraulic oil or compressed air, the fluid hoses preferably being combined into a hose bundle. The hose bundle can also include an air hose if the extruder unit has a seam preheating device in which air delivered through the air hose is heated and delivered to the seam region. There also exists the possibility of integrating into the hose bundle a rod delivery hose for delivering the plastic material in rod form. If the extruder unit requires a supply of electricity, for example for an air heating device and/or for the control system for the fluid motor, the hose bundle can also contain at least one electrical line. The concept underlying these features is that of eliminating from the extruder unit itself, to the greatest extent possible, all devices that might increase its weight or volume.
In a further embodiment of the invention, provision is made for a pressurized fluid generator, for example a hydraulic pump or a compressed air generator, to be attached to the ends of the fluid hoses remote from the extruder, for example to be arranged in a housing mounted on casters. This allows the extruder welding device to be used at any desired location, provided only that energy is available for operating the pressurized fluid generator. The pressurized fluid generator preferably has a receptacle for a reel of rod made of the plastic material, and also an air supply device that is connected via an air hose to the extruder unit. This does not exclude the possibility that the air supply device and/or the receptacle for the rod reel are arranged on the extruder unit itself. What must then be accepted, however, is the disadvantage that the weight and volume of the extruder unit are thereby increased.
In a further embodiment of the invention, provision is made for a rotation speed control device for adjusting the rotation speed of the fluid motor to be provided. With hydraulic motors in particular, a rotation speed control device of this kind is easy to set up. The rotation speed control device can have a bypass controller that is arranged on the fluid motor and/or on a pressurized fluid generator connected to the fluid motor. Alternatively, the rotation speed control device can also have a rotation speed controller for a pressurized fluid generator connected to the fluid motor. The rotation speed control device can have a rotation speed adjustment device on the extruder unit that is connected via a control line to the rotation speed control device. The rotation speed control device should preferably have a control loop to stabilize the rotation speed that is set.